The organizing principle of “The Great Wall” is Lots—lots of Chinese and American money lavished on a remarkably dull spectacle in which lots of medieval Chinese soldiers, plus a European mercenary played by Matt Damon, struggle to repel successive attacks from lots—and we’re talking in the zillions now—of ravening, slavering beasts that behave a lot like zombies. The Great Wall of China wasn’t built to keep out the Mongol hordes, as we’ve been told, but to keep out these digital hordes (who were not, as far as we’re told, asked to finance its construction). That isn’t a bad idea for a fantasy, but the...